1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus having a function of analyzing a type of information of image data that is to be printed on a recording sheet and determining a shape and a printing position of a see-through preventing pattern corresponding to the image data to be printed.
2. Description of the Related Art
There may be the case in which, when a copied matter copied onto a white paper by a copier, which is one type of an image forming apparatus, is put in an envelope, the content of the copied matter can be seen through the envelope. Various methods have been used, such as a method of using an envelope that is specially processed, a method of using a thick paper, a method of using a special paper having special pattern on the back surface thereof, a method of printing the whole back surface of a general recording sheet solid with ink or toner, etc. in order to prevent the action of holding up the envelope against light to see the information in the envelope and enhance confidentiality of the copied matter.
For example, the Japanese Unexamined Patent Publication No. 2001-171264 discloses a overlapped adhesive sheet that employs a special sheet and in which the position of the see-through preventing printing is improved, in order to enhance the confidentiality of printed information and reduce sheet feeding trouble. The overlapped adhesive sheet is a concealed postcard folded in three having three sheets connected, wherein the see-through preventing printing is not performed on the second piece of sheet at the central part, but the see-through preventing printing is performed on the back surface, which is not the surface on which the information is printed, of the first and third pieces of sheets at both sides, in order to achieve enhancement of the confidentiality and reduction in the sheet feeding trouble.
However, in the method of using a special envelope or sheet, the degree of freedom of selecting an envelope or sheet is reduced. Further, since the cost of the envelope or sheet itself is expensive, this method leads to increased cost. In the method of printing the whole back surface of a general sheet solid, ink or toner is consumed in an amount greater than the amount used for printing on the front surface, and further, the deterioration of the consumables in the printing apparatus is accelerated, so that the maintenance cost is increased. In the method of printing the whole back surface solid with ink or toner, the resistance between a sheet feed roller and the sheet is increased after the printing on the back surface, which causes a paper jamming due to the sheet wound around the roller.
The sheet disclosed in the Japanese Unexamined Patent Publication No. 2001-171264 is effective for the special sheet that is the sheet folded in three, and it is difficult to adopt this method to a standard white sheet of A4 size. When an A4 sheet is put in an envelope without being folded, it is unclear which position on the back surface of the A4 sheet the see-through preventing printing should be performed, with the result that the position and shape (size) of the see-through preventing printing for reducing the sheet feeding trouble cannot be determined.